This invention is directed to crystalline forms of 1-methylcarbapenem compounds that exhibit excellent antibiotic activity against various bacterial strains and are stable enough to keep for a long time, and have high producability or handling ease. This invention is directed to medicaments containing a crystalline form of the present invention as an active ingredient (and particularly pharmaceutical compositions for the prevention or treatment of bacterial infections). This invention is directed to the use of a crystalline form of the present invention for the manufacture of a medicament for the prevention or treatment of bacterial infections. This invention is directed to methods for preventing or treating bacterial infections which comprise administering an effective amount of a crystalline form of the present invention to a warm-blooded animal in need of such prevention or treatment. Further this invention is directed to processes for the preparation of crystalline forms of the present invention.